US President Donald Trump on Friday said a military option against North Korea was "locked and loaded," his latest salvo in an escalating war of words with Pyongyang's nuclear-armed regime.

"Military solutions are now fully in place, locked and loaded, should North Korea act unwisely. Hopefully Kim Jong Un will find another path!" Trump tweeted.

The US president's Twitter missive ratcheted up his already bellicose rhetoric with Kim over North Korea's weapons program, as Beijing appealed to the two leaders to dampen their fiery exchange.

A day prior Trump had hardened his warning that Pyongyang would face "fire and fury" if it kept threatening the United States, saying maybe his tough talk "wasn't tough enough."

Trump also warned North Korea it should be "very, very nervous" of the consequences if it even thinks of attacking US soil, after Pyongyang said it was readying plans to launch missiles towards the Pacific territory of Guam.

Pyongyang said the scheme to target the island, a key US military outpost in the western Pacific, was intended to "signal a crucial warning" as "only absolute force" would have an effect on a US leader "bereft of reason."

Beijing on Friday pleaded with the US and North Korea for restraint, urging the two parties "to be cautious with their words and actions."

China has repeatedly urged a resumption of long-dormant six-party talks to peacefully resolve the crisis, but its position has been overshadowed by the emerging brinkmanship between Trump and Kim.